Feedwater system



A. J. ALIX FEEDWATER SYSTEM July 10, 1962 Filed Sept. 29, 1959 INVENTOR.

H'r'thur HZI'X BY j H o'r'ney Yw' A United States Patent Corporation, Worcester, Mass, a corporation of Massachusetts Filed Sept. 29, 1959, Ser. No. 843,188 5 Claims. ((31. 122-459) This invention relates to a feedwater system, and more particularly to apparatus arranged to heat feedwater before introduction into a steam generating unit.

In a steam generating unit is is common practice to heat the feedwater which is to be introduced into the Steamand-water drum of the unit by passing it through a heat exchanger called an economizer over the exterior surface of which pass the combustion gases leaving the steam generating unit. This system has the advantage, of course, of increasing the eificiency of the unit by reducing the temperature of the gases leaving the stack. After passing through the economizer, it is common practice to pass the feedwater into the steam-and-water drum and at the same time to use it for increasing the purity of the steam leaving the steam-in-water drum and going to the superheater. One common practice is to use a so-called condenser which is a heat exchanger located in the steamand-water drum over which the steam passes and which contains the relatively cool feedwater. However, in these previously-known arrangements the economizer has been subjected to a considerable amount of corrosion, mainly due to the fact that, because of the very cold temperature of the feedwater passing through it, the gas temperature at certain portions of the economizer drops below the dew point of certain corrosive substances in the gas, which substances are believed to be in the nature of sulphuric acid and the like. At the same time, a difficulty has arisen due to the fact that the water, after it has passed through the economizer, is quite warm, and this makes the condensers less than efiicient. In connection with the condenser also it has been impossible to determine the amount of condensation which has taken place on the outside of the condenser due to the difiiculty of measuring the ingoing and outgoing temperatures of the feed water in the condenser. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore,v an outstanding object of the present invention to provide a feedwater system in which economizer corrosion is reduced to a minimum.

Another object of this inventionis the provision of a feedwater system in which the effectiveness of condensers in the steam-and-water drum of a steam generating unit is increased to increase the purity of steam resulting therefrom.v

A further object of the present invention is the provision of a feedwater system which permits the measurement of the efliciency of condensers in the steam-and-water drum of a steam generating unit. I

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to certain of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a transverse sectional vew of a steam-andwater drum of asteam generating unit embodying the principles of the present invention; and

FIG. 2 is a sectional, somewhat schematic view of the unit taken longitudinally of the steam-and-water drum.

For the purposes of the present invention the. expression longitudinal shall be used to indicate a direction along the axis of the steam-and-water drum, while the expression transverse will be used to indicate a direction at a right angle to the said axis.

In the drawings, the feedwater system, indicated generally by the reference numeral 10, is shown in use in connection with a steam-and-water drum 11, forming part of a conventional steam generating unit. A body of water 12 is shown residing in the lower part of the drum. Leaving the lower part of the drum are downcomers 13, and at the right side are steam release tubes 14. Tubes are provided for carrying steam from the upper part of the steam-and-water drum to the superheater (not shown). Located adjacent the steam release tubes 14 is a primary separator 16. At the other part of the drum adjacent the superheated steam tube 15 is a dryer carton 17 having a drain tube 18 leading downwardly therefrom. Located along the length of the drum to the left of the drain tube 18 is a series of condensers 19 of the type shown and described in the patent to Andrews No. 2,424,212, issued July 22, 1947. Each condenser consists of a generally inverted U-shaped tube with at least one of the vertical lengths being covered with surface-extending fins. One end 21 of the condenser discharges feedwater into the body of water 12. The end of the condenser opposite the end 19 is connected into a feedwater distributing pipe 22 which is an elongated hairpin-shaped aifair having an end 23 extending outwardly of the drum 11 at one end. Surrounding the feedwater distributing pipe 22 is a jacket 24, the jacket having two ends which extend outwardly of the same end of the drum 11. As is particularly evident in FIG. 1, the feedwater distributing pipe 22 is covered with surface-extending fins 25 and extend outwardly adjacent pipe and approach the surface ofthe pipe itself. The upper portion of. the jacket 24 extends outwardly of the drum 11 and is connected to a cold water line 27, while the other end is connected by a line 28 to the hot side of an economizer 29, which is the side over which the gas passes first. The lower part of the jacket 28 extends outwardly of the drum '11 and is-connected by a line 28 to the lower or'cold end of an economizer 29; this is the end over which the gas passes last. The upper end of the economizer or the hot end. is connected by a line 31 to the end 23 of the feedwater distributing pipe.

Operation of the invention will now be readily understood in view of the above description. Cold water enters the system by passing from the line 27. into the upper end of the jacket 24. It flows over the outer finned surface of the feedwater distributing pipe 22 and eventually leaves through the line 28 to connect to the lower end of the economizer 29. It flows through the economizer in counterflow to the direction of flow of gases; the feedwater leaves the upper end of the economizer through the line 31 and enters the end 23 of the feedwater distributing pipe 22. It leaves the upper part of the distributing pipe and flows into the body of water in the steam-and-water drum but first passingthrough the condensers 19. Because of the provision of the fins '25 and 26 on the outer surface of the feedwater distributing pipe '22 and the inner surface of the jacket 24, respectively, the heat exchange between the liquids is quite substantial. The feedwater distributing pipe 22 contains, of course, water which is to be immediately passed through the condensers 19;. It has been cooled by heat exhange relationship with the cool water coming from the line 27. Thewater passing through the jacket 24 is warmed up by coming into heat exchange relationship with the water in the distributing pipe 22 which has already passed through the economizer 29 and has, therefore, bee heated. The net eifectof thisheat exchange is that the water entering the lower end of the economizer 29 and passing upwardly in counterflow heat exchange relationship with thegases is warmer than the Water entering from the pipe 27 so that the likelihood of condensation of corrosive material from the gases on the outer surface of the cold end tubes of the economizer is minimized. On the other hand, the water which passes through the condensers 19 has been cooled at the last minute by coming into heat exchange relationship with the water in the jacket '24 so that it is colder than might ptherwise be true. It can be seen, then, that by use of the present feedwater system that it is possible to reduce economizer corrosion, to increase the purity of the steam leaving the steam-and-water drum 1'1, and to measure the efiiciency of the condensers. This last benefit is obtained because of the fact that the water entering and leaving'through the'end wall of the drum 11 is available for temperature readings so that one can determine the efficiency of the heat exchange relationships.

It is obvious that minor changes may be made in the.

comprising I (a) a steam-and-Water drum,

(b) means defining a gas'flow passage, (c) an economizer positioned in said gas flow passage with one end downstream of the other end, (d) a series of steam condensers mounted in the drum,

(e) a heat exchanger consisting of a first U-shaped tube connected at one end to the said other end of the I economizer over which the combustion gases first pass, a second U-shaped tube connecting a source of 'cold'feed water to the said one end of the economizer over which the combustion gases last pass, and heat exchange means for causing the heat to pass from the water in the first tube to water in the second tube, the said other end of the economizer discharging into the heat exchanger, the condensers being connected to the other end of the first U-shaped tube and receiving feed water from the economizer after it passes through the heat exchanger in heat exchange relationship to the incoming feed water. 2. A feed-water system for a steam'generating unit, comprising (a) a steam-and-water drum, (b) means defining a gas flow passage, (0) aneconomizer positioned in said gas flow passage with one end downstream of the other end, (d) a series of steam condensers mounted in the drum,

(e) a heat exchanger mounted in the drum, the heat 1.,A' feed Water system for a steam generating unit,

exchanger consisting of a first U-shaped tube connected at one end to the said other end of the economizer over which the combustion gases first pass, a second U-shaped tube connecting a source of cold feed water to the said one end of the economizer over which the combustion gas is lastpassed, and heat exchange means for causing the heat to pass from the water in the first tube to the water in the second tube, the exit end of the economizer discharging into the heat exchanger, the condensers being connected to the other end of the first U-shaped tube and receiving-feed water from the economizer after it passes through the heat exchanger in heat exchange relationship to incoming feed water. 3. A feed water system for asteam generating unit, comprising 7 (a) a steam-and-water drum,

(b) means defining a gas flow passage,

(c) an economizer positioned'in said gas flow passage with one end downstream of the other end,

(d) a series of steam condensers mounted in the tube,

(e) a heat exchanger consisting of a first U-shaped tube connected at one end to the said other end of the economizer over which the combustion gases first pass, a second U-shaped tube concentric with the first tube connectng a source of cold feed Water to the said one end of vthe economizer over which the combustion gases last passed, and heat exchange means for causing the heat to pass from. the water in the first tube to the water in the second tube, the said other end of the economizer discharging into the heat exchanger, the condensers being connected to the other end of the first U-shaped tube and receiving feed water from the economizer after it passes through the heat exchanger in heat exchange relationship to incoming feed water.

4. A feed water system for a steam generating unit, comprising a (a) a steam-and-water drum,

(b) means defining a gas fiow passage. (c) an economizer positioned in said gas flow passage with one end downstream of the other end, (d) a series of steam condensers mounted in the drum, (e) a heat exchanger mounted in the drum, the heat exchanger consisting of a first U-shaped tube connected at one end to the said other end of thejenconomizer over which the combustion gases first pass, a second U-shaped tube concentric with the first tube connectinga source of cold feed water to the said one end of the economizer over which the combustion gas is last passed, and heat exchange means for causing the heat to' pass from water in the first tube to the water in the second tube, the said other end of the economizer discharging into the heat exchanger, the condensers being connected to the other end of the first U-shaped tube and receiving feed water from the economizer after it passes through the heat exchanger in heat exchange relationship to incoming feed water. t

1 5. A feed water system for a steam generating unit, comprising 7 v (a) a steam and-water drum, (b) means defining a gas flow passage, 7 (c) an economizer positioned in said gas flow, passage with one end downstream of the other end, (d) a series of steam condensers mounted in the drum, (2) a heat exchanger consisting of a tube connected at one end to the said other end of the economizer over which the combustion gases first flow, a second tube connecting a source of cold feed water to the said one end of the economizer over which the combustion gases last pass, and heat exchange means for causing the heat to pass from the Water in the first tube to water in the second tube, the said other end of the economizer discharging into the heat exchanger, the condensers being connected to the other end of the first tube and receiving feed water from the economizer after it passes through the heat exchanger in heat'exchange relationship to the incoming feed water. 7

References Cited in the file of this patent I UNITED STATES PATENTS 669,921 Gibson Mar. 12, 1901 2,114,223 'Jacobus Apr; 12, 1938 2,256,115 Hobbs Sept. 16, 1941 2,424,212 Andrews etal. July 22, 1947 2,527,450 Rehm Oct. 24, 1950 FOREIGN PATENTS 571,320 Germany Feb. 27, 193 3 

